The Game
by Rocksteady Betty
Summary: Casey and Derek engage in a competition of abstinence, which starts to do funny things with how they see each other.
1. Chapter 1

**A/N:** I started this years ago, and come back to it every so often. I have a few chapters to post, and depending on your interest, do hope to finish it. Post Vacation with Derek.

* * *

Casey put the finishing touches on her makeup and examined herself critically: hair loose, dress just snug enough to really get his attention. Not bad, she thought, and headed downstairs to meet her date. "How do I look?" Her roommate, Lisa, looked up from the pile of books spread over the dining table. "Hot," she nodded approvingly.

"You look better without all that makeup shit."

Casey turned in disbelief to the couch where Derek was sprawled, a half-empty bag of _her _chips in his lap, watching a hockey game. "And you look better at your _own house_," she snapped. "Why are you here?" He didn't take his eyes off the game. "Because it's my mission in life to make you miserable?"

"Mission accomplished. Go home."

"Nah, I'm good here."

Casey yanked on her shoes and shot Lisa a dirty look. "Why did you let him in?"

"Didn't. He was here when I came in."

"Door was open," he said as the game went to intermission and he went to root through the fridge. Casey gaped at him. "Even after all these years your audacity astounds me."

"I thought I left some beer in here last week."

"Oh, that was yours?" Lisa said, but was paid no attention. Derek kicked the door of the fridge shut and dumped the makings of a sandwich on the counter. "There was a minor incident at my place. Figured it was a good idea to clear out for awhile."

"Let me guess, that minor incident involved you and someone's girlfriend."

"She _said _they were broken up."

Casey rolled her eyes. "You're unbelievable. What about your precious guy code?"

"Huh?"

"Duh. Remember that whole thing with Sam?"

"Oh, right. That was about sisters. Mostly I just didn't want _you_ dating my friends."

Casey snorted, but she'd never wanted him dating her friends either so left it alone. Derek took his plate back to the couch, dropping a sandwich in front of Lisa on the way. "So, who's getting lucky tonight?"

"What?!"

"C'mon Case, you've got the slutty shoes on. Usually means you're out to get some."

"Screw you! Seriously, you need to leave. Now."

"Well this sandwich isn't going to eat itself…"

"I love how you manage to ruin my night before it even starts."

"Cry me a river, Princess," he mocked, and turned up the volume as the game resumed. Since he looked like he was settling into the couch for the long haul she grabbed the remote, switched the channel, and pulled the batteries out – something years of experience had taught her. That had him on his feet. "Casey, change it back. Now. This is a crucial game."

She tossed the empty remote at him. "This is me not caring. You could always change it by hand – oh, wait, you can't because _you _busted the TV last time. Guess you'll have to watch it somewhere else."

"Casey," Derek said dangerously. "Give me those batteries."

"Derek," Casey replied sweetly. "You can kiss my ass."

That was all the invitation he needed to spring over the coffee table and tackle her in an attempt to get them back, but she knew his game and dodged the attack. It didn't take long before they were wrestling over a pair of lousy batteries and Derek hooked her behind the knee with his foot and they toppled to the floor. He was just about to pull her fingers apart when she bit his hand. He let go with a yelp and she used that moment to stuff the batteries down her top. "HA!" she grinned triumphantly. There was one line Derek would never cross with her – her hemline. She could see the indecision written all over his face and used his hesitation to elbow him off of her. It was when she was back on her feet that he blindsided her and stuck his hand right down the front of her dress. "Der-EK!" she shrieked, and in that moment noticed Justin, her date, in the open doorway with Lisa. He didn't look impressed. "Am I interrupting?"

Casey shoved Derek away and barely noticed when he tripped over a cushion and ended up on his ass. "Justin, hi! No, just a minor disagreement. Let me grab my jacket." She went to find her coat in the kitchen and fished the batteries out of her bra on the way. Derek followed.

"You're wearing the fuck-me shoes for that asshole?"

She opened the back door and threw the batteries out into the dark. "Go fetch."

* * *

The post-game interviews were still going on when Casey got home. Lisa hadn't moved from the table and Derek was once again sprawled across the couch. She shoved his feet out of the way and collapsed in a huff. He muted the TV. "That was quick."

She pulled off her shoes. "He _was _an asshole."

"You've gotta stop looking for Prince Charming when you just want to get laid, Spacey."

"You're such a pig. Unlike _you_ I do not consider casual sex a sport."

"Yes you do, you just call it 'dating'."

"Oh, what_ever_! I'm not going to sit here and let someone who spent an entire year whoring around Europe judge me."

"As opposed to the year you spent whoring around New York?"

"You _mother_\- you know goddamn _well-"_

Derek held up his hands in surrender. "Don't get your panties in a twist, Princess. All I'm saying is that you aren't really in a position to judge either. How many guys have you been out with since the semester started?" She was fuming but couldn't help but do the math. Derek took her silence as an assent. "That's what I thought." She tried not to pout. "I have no problem being single whereas you get the shakes if you can't feel up some bimbo every other day."

"Well thanks to you I filled my quota tonight," he said nastily.

"You know you're hard up when you cop a feel from your sister," Lisa interjected.

"STEP!" they snapped immediately. Lisa shrugged. "Same difference." But they'd already forgotten her. Casey sneered. "I could outlast you any day of the week." Derek leaned in, eyes narrowed. "Is that a challenge?" They were practically nose-to-nose now. "What do you think?"

"I think you're getting into some dangerous territory."

"Afraid you can't handle it, Der? Because I'm not just talking about sex. I mean no dating, no sex, and nothing in between. You so much as touch a girl, you lose." They stared each other down for a moment, then he got that self-satisfied smirk that she hated so much and leaned back. "This'll be too easy."

"I think you're fooling yourself," Casey said honestly, then turned to Lisa. "You're witness to this. It starts right now."

"I'll make a note of it," was the dry response. Derek got his stuff together and headed for the door. "Oh, Case, we still on for that study session tomorrow night?"

"Yep. I made some extra notes for you."

"Thanks. Lock up behind me, I don't want any weirdos off the street coming in. Night Lisa," he called. "And Casey? Game on."

Lisa looked rather bemused. "I do _not _get the two of you." Casey was perplexed. "What's to get? Anyway, I'm gonna go run a bath. Night!" Lisa watched Casey head up the stairs and could only shake her head.

* * *

The first two weeks were a breeze, but by the third Derek was beginning to lose his resolve. It seemed like every girl on campus knew of his bet with Casey and was crawling out of the woodwork to tempt him. The most startling thing was that this was probably the single most important competition he'd ever had with Casey. Whoever won this one would be the dominant player in their relationship from then on. It was not a challenge he intended on losing. He just needed a good motivator to keep his head in the game. Then, midway through the third week fate intervened. Lisa happened to mention that their third roommate had moved out and there was an available room in their house. This came at the perfect time as the situation with his own roommate's girlfriend had only gotten worse, _and _it was the perfect way to get under Casey's skin. They hadn't lived under the same roof for four years, but he figured that old habits died hard.

He made a point of moving his stuff in on the night Casey taught her dance class so that he'd have the advantage of surprise. When she came in later that night, he was in his new room doing some work on his laptop. He'd made sure to keep the door wide open as she'd have to pass it to get to her own, and he was not disappointed. He heard her come up the stairs, heard her walk down the hall and pass his door, heard her stop, and only did he look up when she marched through the door.

"What the fuck?"

It was better than he expected. She looked furious and completely confused at the same time, and he always knew he'd got to her when she swore. "Hey Case," he grinned brightly. "Good class tonight?"

"_What _are you doing?"

"Homework. Why?"

Her nostrils flared and she fisted her hands on her hips, and he nearly laughed aloud. "Ohh, you mean what am I doing here? I'm your new roomie!" Her jaw nearly hit the floor. "Like hell you are."

"What, you think I'd go so far as to move all my stuff in here just for the fun of it?"

"That's exactly what I think. This is just the kind of stupid prank you'd pull."

"Well if you want to call Barry and check, be my guest, but could you do it somewhere else? You're pretty ripe at the moment and I've got to get this paper finished." All she could do was growl in frustration and storm out of the room. "Aw, come on Casey, it's just like old times!" he called after her gleefully. "We're even sharing a wall again!"

Her door slammed so hard that his window rattled.

* * *

It was well after midnight that same night when Derek realized there was a minor, unexpected flaw in his plan. He'd gone down to the kitchen for a snack and found the lights blazing, the radio on low, and Casey standing tiptoe on a kitchen chair while she rooted through a top cupboard. "What are you doing?" She jumped, startled, but barely spared him a glance over her shoulder. "Working out my frustration creatively," she said through clenched teeth. He ambled over to the fridge and then noticed that the countertop was covered with dishes and various boxes of food. "You're cleaning."

"Organizing," she said shortly. Derek rolled his eyes. "Your OCD's showing big time, Space." And then he realized that that wasn't all that was showing. She was wearing some flimsy tank top and a ratty pair of shorts; nothing he hadn't seen before, except this was the first time he noticed just how short her shorts were. When she reached up to the highest part of the shelf, those shorts dipped down so low he wondered if she was even wearing underwear. He was immediately mortified at the thought, but was having a very hard time tearing his gaze off of the smooth skin on her abdomen. When those shorts of hers drooped just a little lower to reveal her summer tan line he knew there was no way she was wearing underwear, and he nearly dropped the carton of juice he was drinking from.

And then, when he didn't think it could get any worse, he noticed something else. A few loopy black lines peeked over the very low waistband of those shorts and Derek choked on the orange juice. "Is that a _tattoo_?" He spluttered after the worst of the coughing had subsided. Before he knew what he was doing, he was reaching out and his fingers brushed her skin, intent on edging down those shorts to get a look at the _tattoo _that _Casey _had and never told him about. For a split second – barely a heartbeat – he let his thumb stroke that little bit of skin and watched the goosebumps raise in its wake, then he heard the sharp intake of breath from her and realized what he was doing. He snatched his hand away as if he'd scalded it.

_Oh holy fuck. _He tried desperately to cover that inexplicable moment in which he'd lost his mind. "_You _have a tattoo?" he demanded, attempting his usual bravado. He could see the wariness in her eyes, and he hoped to God she would think it was nothing. "Not that it's any of your business," she began stiffly. "But yes."

"What is it?"

She pursed her lips for a moment, then smirked. "That's for me to know." He nearly deflated with relief. He didn't bother with a retort before making a hasty retreat to his room. The flaw in his plan, he acknowledged, was that he was enduring a self-imposed term of abstinence while living in a house with a girl who cleaned the kitchen in the middle of the night in the smallest shorts imaginable, had secret tattoos, and had got goosebumps when he'd touched her. Never mind that that girl was his own step-sister; the same step-sister he'd shared a house with for four years and never so much had an erotic dream about. He'd never before admitted to himself a very unsettling truth: Casey was attractive, and he was in trouble.


	2. Chapter 2

She hated him. Him and this stupid game they were playing. It didn't matter that she'd started it; she'd _never_ expected him to last a week, let alone the four that they were going on. It was getting to him though, she reasoned to herself over the textbook she was supposed to be studying. After that weird moment in the kitchen the other night he'd been especially short-tempered and took any opportunity he could to pick fights. Even Lisa wasn't safe from his attitude. But it was getting to her too, and that was the problem. She'd gotten a little tingle when his thumb had brushed her skin that night, and _that _was the only reason she hadn't bashed him in the head with a frying pan. This abstinence thing was starting to do funny things to the both of them, and if she was getting a physical reaction from _Derek_ then there wasn't a chance she'd last too much longer. The game needed to end but she needed to figure out a way to end it and still be the winner. She decided that she needed an objective opinion and called the only person who would possibly understand what was at stake.

"Em, I need your help."

"What's the problem?" Emily asked immediately, and Casey relaxed just a bit. She and Emily had grown apart some over the last few years, but Emily was still willing to drop everything to help, no matter what. "I need to crush Derek."

"Uh, you called me just for that? Isn't that your goal every day?"

"This is different," Casey said seriously, and filled her old friend in on the details of the competition, even telling her about the incident in the kitchen. Emily was silent for a long moment, then: "I think your problem is that you're not actually playing the game. You're just sitting there waiting for him to fail on his own. Maybe you need to be more active in trying to trip him up, you know?" The proverbial light bulb sparked over Casey's head. _Of course_! "Em, you're a genius! Thank you!"

"Anytime. Hey, keep me posted, will you?"

Casey returned to her studying almost gleefully. Emily had been absolutely right: Casey hadn't been playing the game. If she wanted Derek to lose, she was going to have to make it happen.

* * *

The party was raging, the house so full of people they spilled out into the backyard despite the bitter December cold, and Casey sat slumped on the stairs wondering where it had all gone wrong. It had started out simple enough: she'd invited a dozen girls over, had plainly told them the situation with Derek and asked if they'd be willing to help her out. Danielle, a gorgeous redhead from her economics classes, seemed especially keen.

"So you're asking us to try and break Derek Venturi?"

Casey hurried to reassure them. "I'm not asking you to do anything rash, just maybe flirt with him. If the idea makes you uncomfortable, I totally understand-"

"No," Danielle interrupted. "That jerk dated my roommate last year, and her sister. I, personally, would be delighted to knock him down a peg or two… or a flight of stairs," she added as an afterthought. The rest of the girls laughed and no one headed for the door. Casey nearly clapped her hands in joy. The stage was set. "There's drinks in the kitchen, help yourselves. The food should be here soon."

The girls started a dance tournament game using Derek's Xbox, drinks and snacks were flowing, and everyone seemed in great spirits, _especially _when Derek showed up. He'd regarded the house full of women like he was facing a firing squad and his greatest fantasy in the same moment. He pulled Casey aside after tossing his hockey gear down the basement steps. "What's going on?" Casey shrugged and acted mildly annoyed. It was crucial that Derek think he was unwelcome. "Just a little pre-exam stress reliever." She paused and sighed dramatically. "I _suppose _you can hang out if you want. But only if you promise to keep it in your pants. I will not subject my friends to you at your horniest."

Derek set his jaw, stared her down for a moment, and in the blink of an eye turned on his most charming smile. "Thanks, Case, I think I _will _stick around awhile." She huffed and elbowed past him to join the crowd in the living room. She gave the thumbs up to her team and the game was on, and for a while it had worked. Danielle was doing a magnificent job of commanding his attention. At one point she'd leaned in close to whisper something in Derek's ear and Casey could tell he was interested, but then he'd shot a look Casey's way and she cursed under her breath. He'd caught himself in time, excused himself from Danielle and disappeared for a few moments. Half an hour later his entire hockey team had shown up, blowing her plan to hell. It wasn't long before word had spread and half of Kingston showed up on her doorstep - including Jamie Bell, a fellow fourth-year she'd had her eye on _forever_, and wasn't it just so lucky that all of a sudden he was single?

Thus her current situation, hiding from Jamie on the stairs while trying to keep an eye on things to make sure nobody went through a window. Eventually Derek appeared and joined her on the step, nudging her shoulder with his. "Congrats, Case, you're throwing the party of the year." She snorted. "Who'd a thunk it, eh? Keener like me?" He chuckled. "I dunno, you're full of surprises lately." She stifled a yawn. "You too. I didn't think you'd be able to resist a room full of women throwing themselves at you."

"I admit, I'm a little impressed. Never thought you'd play dirty and set a trap. I must finally be rubbing off on you."

"What gave it away? Danielle almost had you at one point."

"It was a good try," he admitted. "But then I realized that you would never throw a party this close to exams unless you had some ulterior motive."

"I hate that you know me so well," she grumbled. "But I'm not nearly as uptight as I used to be."

"No, New York really pulled that stick out of your ass," he agreed and leaned in a little closer. "But it's gonna take a _lot _more than that to break me." She glanced over and saw there wasn't a trace of his usual smug smile. She knew that she'd been underestimating him but he _always_ underestimated her and that would only work to her advantage. She held his gaze steadily, then leaned in so close her lips nearly grazed his ear. "I'm just getting started."

The cops showed up at three (after a discreet call from Lisa, who had an early class) and Casey happily helped them herd the crowd out the door, locking it firmly behind the last couple of stragglers. She decided to leave the mess for the morning and got ready for bed. It was on her way to the bathroom that she passed Derek's door and realized she'd lost track of him after their tête-à-tête on the stairs. The light was still on under the door and she tapped on the frame quietly, hoping that if he ignored her it would mean he wasn't alone in there. To her great disappointment he called for her to come in.

He was on the bed watching a movie on his laptop and she raised her brow slightly at the empty dishes next to him. It seemed he'd been up here longer than she thought. He regarded her expectantly and she crossed the room to settle herself in his desk chair. "Turned out to be a pretty good night," she said amiably. "Have you been hiding up here for long?"

"I came up around the time you started playing beer pong with that Bell guy. I couldn't watch that massacre."

Casey rocked back in the chair. "My beer pong skills are a well-kept secret. I'm still sober…mostly. He had to be carried out, but not before he pledged his undying love for me." Derek grinned, though she could tell it was reluctant. "You don't want to string him along, you know. You can graciously bow out now and I won't hold it against you. Much."

"Not a chance." She paused, then nudged his leg with her toe. "Why are you sticking this out, really?" He studied her foot where it rested by his knee. "For the same reason you are," he said finally.

"Because you think I'm a smug bastard who desperately needs to learn that he is not, in fact, superior to the rest of the human race?"

Derek snorted. "Tell me what you really think."

Casey would have, but when she opened her mouth a yawn came out instead. She stretched sleepily and was about to say goodnight when she noticed where his gaze was focused. Her nightshirt had inched up her thigh when she'd stretched and settled high enough to only cover the essentials, and Derek didn't seem able to tear his eyes away. That look contained something she'd never seen before from him and she felt a little quiver low in her belly. She nearly jumped out of the chair but managed to restrain herself and casually adjusted the shirt before getting to her feet. It didn't seem like he knew she'd caught him looking, and she wasn't about to let on that she had.

* * *

"_I'm_ _just getting started."_

It was all Derek could think of when Casey sauntered out of his room. It had been haunting him since their conversation on the stairs: her voice like honey, her warm breath on his ear, the dark promise in her eyes, the idea that if he'd moved his head a fraction of an inch, his mouth would have been on hers… And then now, that excuse for a nightshirt riding high on her thighs, the way her breasts had strained against the thin cotton when she'd stretched. Jesus fucking Christ. He'd wanted to take her then and there in that stupid chair. His own _sister._

_STEP._

_Same difference._

Except it really wasn't, not anymore.

He woke the next morning aching with thwarted desire and decided that this competition had to end before he did something really stupid. Things had definitely gone too far when he started fantasizing about _Casey_. After a long, particularly cold shower he found Casey scrubbing the carpet in the living room. Trash bags were lined up by the door, and since he was about to concede defeat he went with the spirit of uncharacteristic behaviour and took the bags out. Casey's brows nearly hit her hairline but she didn't make an issue of it. "Thanks."

Derek sighed, it was now or never. "Case, I-"

"Did you know that Lisa's running a pool on our little game?"

"Bullshit."

Casey rocked back on her heels and studied the spot on the carpet that apparently wasn't coming out. "I'm serious. She was taking bets all last night."

"Spectacular." Of course this would happen. He might have been able to live with Casey holding it over his head that he'd given in, but now that it was a matter of public record there was no way his friends would make it easy on him. "What are the odds?"

"Enormously in my favour."

He rolled his eyes. "Naturally."

"You can't be surprised. You've got so many notches in your bedpost it's practically kindling."

"You know, I'm getting really tired of you constantly insinuating that I'm some massive slut. I don't fuck everything that moves." Casey held up her hands in surrender. "Okay, okay, sorry." Derek brushed past her into the kitchen, angrier with himself than her. Why had he told her that? The last thing he wanted to do was make himself look vulnerable. God_damn_ it all!

"What's with all the slamming around?" Casey demanded awhile later after he'd taken out his anger on breakfast preparation. He glared at her and got even more annoyed when he couldn't help but notice how _good _she looked. He usually went for the girls who used all the tricks to pretty themselves up, but there was something about the way Casey looked when she wasn't trying. Standing there in sweats, a hoodie and – were those his socks? "Are those my socks?" To his great surprise, she blushed. "They're way warmer than mine," she said defensively, and again to his surprise, he just laughed. "Whatever, Princess. Keep 'em. Want an omelet?"

He didn't think she'd ever looked more stunned by something he'd said. "Uh, sure?" She took a seat and watched him suspiciously as he whipped up breakfast. "The secret ingredient's not arsenic or something, is it?" He snorted, suddenly and inexplicably in a cheery mood. "You'll just have to trust that poisoning your food is not the way I'd get rid of you."

"Trust you, huh? That'd be a pretty big step in our relationship."

He set a full plate in front of her and shrugged. "Suit yourself, but I make a pretty mean omelet."

"Since when do you cook?" She peered closely at the plate and broke off a tiny piece with her fork. "In the entire time I've known you I have never seen you even turn on the oven." She tentatively tried a bite. "Oh my god, Derek. This is _good_." He grinned as Casey devoured her meal. "You think with the amount I eat that I don't know how to cook a thing or two?"

"Did you just tell me your darkest secret?" she teased.

"That's for me to know," he replied, mimicking her tone from that night in the kitchen. He savoured the memory of touching her when he'd tried for a look at that tattoo of hers. "And what about your darkest secrets?" She stacked his empty plate on hers and smirked as she got up from the table. "You have _no _idea."

_Jesus_. What the hell had gotten into Casey? And him, for that matter. He would have considered that little exchange at the table flirting had it been any other girl, and whether or not he was screwed up enough to currently find his step-sister attractive, _she _had flirted right back. He needed some help, fast.

"Sam," he said seriously when his friend answered the phone. "I am so fucked."

"What's going on?"

Derek collapsed on his bed with mild relief. Sam was and always would be his best friend, and he would definitely know what to do. He explained the situation with Casey and tried not to wince when he admitted that maybe he was attracted to her. "…I don't know why she's acting this way. It's starting to get to me." He could hear the chuckle in Sam's voice when he replied. "Newsflash, Bro: Casey's always been hot. You just never noticed before because you were too busy trying to hate her."

"No, this is different. She used to be annoying and uptight as all hell. Hot maybe, but that other stuff canceled it out. Now she's acting kind of…cool. Stop laughing at me! Fuck!"

Once Sam calmed down he tried to reason. "Dude, maybe she's just grown up a bit. Living in New York for that year had a huge effect on her. Anyway, if it's getting to you so much, maybe you should just give in, let her win."

"Fuck that. You've been no help whatsoever. Thanks."

Sam laughed again, apparently finding this dilemma hugely entertaining. "Sorry, man. Look, think of this as a hockey game. Right now it's 3-0 for her and she's got the puck. Start playing offense."

_Duh_. The light bulb sparked over his head. Put like that he knew exactly what to do. "Thanks Buddy. Hey, see you in a couple weeks." Christmas break was coming up and Derek fully planned to have won this little competition by the time he and Casey had to go back home.


	3. Chapter 3

Classes ended and exams started, yet despite a rigorous study schedule Derek set his plan into motion. It just so happened that he shared a class with that Bell guy, the one Casey had destroyed at beer pong, and Derek had it on good authority that Casey might have a thing for him. So he set up a study group at their place with Bell and a couple other people, planned to share a few handy hints for picking Casey up, and sit back and watch her crumble. It was perfect. His buddy Kevin showed up first and they got to work in the living room while they waited for Jamie Bell to arrive. Derek was bent over his cue cards scribbling some notes when Casey came down the stairs.

"Don't mind me."

Derek glanced over and did an honest-to-god double take. Casey was hurrying by in nothing but her underwear. It wasn't any more scandalous than a bikini; perhaps the plain cotton set was even less revealing than what she wore in the summer, but there was something extremely intimate about it. He watched her until she disappeared down the basement steps.

"Dude," Kevin said. "Who was _that_?" Derek shook his head. "I have no idea," he muttered. The Casey he knew was not the type to prance around in front of strangers in her underwear. It was a ballsy move.

"You don't know?"

"What? No, forget about it. She's off-limits."

Casey came back up toting a full laundry basket and this time, thankfully, she was dressed. "How's the studying going?" she asked cheerfully. Derek glared, Kevin grinned hopefully. "Great, want to join us?"

"Can't, I'm studying for my Econ exam, then I have to work. Thanks though!"

Derek managed to stay in his seat for maybe thirty seconds after she'd gone up the stairs before jumping up after her. She was folding laundry when he burst through the door to her room. "What the hell was that?"

"What the hell was what?" she replied with exaggerated patience.

"That little show you put on just now in your underwear."

She rolled her eyes. "Well _excuse _me, your Highness. If I want to walk around this house butt naked that's my choice, but as it happens my clothes were in the wash and I didn't expect anyone to be downstairs. I'm so sorry I offended your delicate sensibilities." Her tone dripped sarcasm and defiance, and after a moment he couldn't help himself from sauntering over to her and giving her a slow, deliberate once-over. "I'm sure I'll survive. Kevin not so much. That's a cute little bra you've got, by the way." She raised a brow. "I thought your only concern with bras was taking them off."

_Don't tempt me_. She was too close all of a sudden. They were standing only inches apart and the energy between them had taken on a different life. He could feel it, and by the way her pupils dilated, she noticed it too. For a split second he wanted to dig his fingers into her hair and yank her against him. His blood was pumping and her eyes dropped to his mouth, and then-

The doorbell rang.

_Oh, thank god._

Casey waited until Derek had disappeared out the door before exhaling heavily. Her heart was still pounding. If that doorbell hadn't rung what would have happened? He wanted to kiss her, she was almost sure of it. Finally she let herself smile. It was working! She'd been fully aware that Derek would be there when she'd worn her underwear around the house. She hadn't expected it to work, not really, but he'd taken the bait magnificently. She'd gotten the idea the other night after the party, when he'd looked at her _that _way in his room. Obviously he was on the brink of failure when he started seeing _her _as attractive, so she'd decided to help him over the edge. It might require some tasteless personal sacrifice, but all was fair in love and war, right? Never mind that just now she'd nearly quivered with the need for him to kiss her. And then there was that time in the kitchen when he'd touched her and her legs had gone weak. She wasn't too proud to admit she wasn't impervious to the tension that had sprung up between them all of a sudden, she was just confident enough that he would succumb first.

* * *

It was after one in the morning when Derek got off work, and he tried to be quiet as he made his way up the stairs. The consideration turned out to be pointless as Lisa's door was open and her room empty, and the light was blazing in Casey's. He peered around the door frame to say good night and saw her pacing with a handful of multi-coloured cards and the manic look she used to get in high school at exam time. "Casey," he said slowly, approaching her as carefully as he would a wild cat. "How long have you been studying?" She didn't acknowledge him, but in this instance he figured she was so focused that she hadn't heard him. He strode across the room and grabbed the notes from her hand.

"Hey!" she said indignantly. "What are you doing? Give those back!"

He ignored the demand. "Casey, how long have you been studying?"

"I don't know, a few hours. Since lunch. Give them back, I have to review for my exam tomorrow!" Derek sighed and stuffed the notes in his pocket. "Case, it's nearly two. In the _morning_," he stressed. "You've studied enough. You know everything and you're not going to fail. Say it with me." She glared but grumbled the mantra he'd developed for her years ago. "Fine. I'm not going to fail."

"Good girl," he said and reached up to knead her shoulders. "Christ, you're like a plank of wood," he muttered. "You really need to learn how to relax, Space." Even as he said it he could feel the tension seep out of her as she leaned into him just a little. He caught sight of their reflection in the mirror on her closet door: her eyes were closed and she was almost smiling, and he looked like the devil on her shoulder. He caught his own eyes in the mirror and grinned – why waste such a golden opportunity? As he massaged the muscles at the base of her neck he couldn't help but wonder just how sensitive she was, so he abandoned the massage to lightly trail his fingers down the side of her neck. He glanced back to the mirror to gauge her reaction and found her watching him with an unreadable look in her eyes. He didn't tear his eyes from hers as he slowly skimmed his hands across her shoulders and down her arms, over her hips and her stomach, and it was only as his thumbs grazed the sides of her breasts did she reach up to grasp his hands. "I should get some sleep," she said quietly. He held her gaze for a moment longer before turning wordlessly to go back to his own room. Like he was going to sleep after _that_.

* * *

Derek got up at noon after tossing and turning restlessly for hours, and by then Casey had already finished writing her exam. He was in a foul mood and was itching for a fight. He eventually found Casey outside shoveling the sidewalk and he scowled when she started clearing their elderly neighbour's driveway. _Saint Casey_, he thought with a sneer, not feeling charitable enough to admit he would have done the same for the old lady. Impulsively he put on his jacket and threw open the door to grab a handful of snow off the railing and launch it at her. His aim was on the mark.

"Der-ek!" Casey dropped the shovel and dug the snowball out of the collar of her jacket. He grinned maliciously and threw another one. "Oh my god, are you a _child_?" Casey shrieked, but it was enough to get her to heave one back. He didn't bother to duck – he knew what her aim was like, so he was greatly surprised when he got a mouthful of snow. Casey nearly collapsed in a fit of giggles.

Just like when they'd fought over batteries in the living room, he jumped the steps and ran to tackle her to the ground. This time he was successful, mostly because she was doubled over laughing, but despite that she managed to get another handful of snow as they hit the ground and stuffed it down the front of his shirt. He hissed as the ice cold hit his skin and tried to pin her down to return the favour, but she wriggled out of his grasp. They wrestled around a bit, culminating with Casey sitting on him, a triumphant gleam in her eyes. "Ha!"

Derek was suddenly reminded of the very different kind of look she'd given him the night before, and that memory combined with the way she was straddling him now was about to result in a rather awkward situation. Fortunately he had plenty of experience in this particular arena and quickly and expertly flipped her onto her back. She smirked up at him. "You've done that a few times, huh?"

Apparently they weren't going to acknowledge what had happened the night before, and that was fine with him. He was content with fighting with her if nothing else. "Probably as often as you've wound up on your back." She got that indignant look that usually meant a lecture was imminent, but he was saved when their neighbour poked her head out the door. "Hey you two, when you're done fooling around come on over for some hot chocolate!"

Casey didn't take her eyes off his. "Thanks Roberta, that sounds great!" she called, but he was distracted by the way she'd slid her knee between his legs. Distracted, but not stupid, and he rolled off of her just as she was about to bring her knee up sharply into his crotch. "Careful Princess," he warned lowly. "I didn't take you for suicidal." Casey stuck out her tongue, pelted him with one last snowball, and high-tailed it over to Roberta's.

* * *

This was turning into a disaster of epic proportions. Casey scowled into her mug as Derek shamelessly flirted with Roberta and for the umpteenth time in the past few days, she tried to figure out where she'd gone wrong. It was all Derek's fault, that much was obvious. If he wasn't so damned stubborn and had screwed up weeks ago like he was _supposed_ to, neither of them would be in this mess. She hated to admit it but her plan wasn't working out how she'd hoped. She wasn't an idiot, she knew she was getting to him in a big way, but the problem was she wasn't so sure of her motivation anymore. Since when did trying to get Derek to lose a bet involve letting him run his hands all over her?

Since when did she want him to?

That thought hit her like a freight train and she wanted to bury her face in her hands, but contented herself with glaring daggers at Derek's back. Her anger wasn't enough, however, to drag her mind away from what just a whisper of a touch from him had felt like, and then what it might have been like if she hadn't stopped him…

She got lost in the fantasy for a moment and was rewarded with an elbow to her ribs. "Earth to Spacey," Derek said snidely, and Casey couldn't fight the blush that crawled into her cheeks. She tried to ignore him and shrugged apologetically to Roberta. "Sorry, I was just thinking about my exam this morning."

"I'm sure you did just fine, Dear," Roberta said kindly. "I was asking if you're looking forward to your vacation back home. You leave in a few days, don't you?"

"Yeah, Friday." She hadn't realized it, but Friday was only four days away. They had never set any real parameters around their bet, but something in Casey was determined to have this game resolved before the drive back to London. That meant she had four days to either break Derek or get him to agree to a truce, and honestly she wasn't sure she had what it would take to accomplish either. Breaking him technically meant he'd have to hook up with another girl and suddenly that didn't seem like such a great idea. Casey could barely stop her jaw dropping at the thought. God, was she _jealous _of some faceless girl that Derek had yet to meet?

The thought made her stomach turn and she frowned uneasily. "I'm sorry, Roberta, I have to go. I'm suddenly not feeling well." She refused to meet Derek's eye as she pulled on her jacket and hurried out the door. By the time she made it across the lawn to her own place she was ready to throw in the towel. _Nothing _was worth being jealous of a Derek Venturi conquest.

"Hey Case," Lisa said cheerfully, then caught sight of Casey's expression. "What's wrong?"

"I give up, that's what. I can't do this anymore! He can have it."

"Casey, no!" Lisa admonished and led her to the couch. "You can't let him win just because you're horny." Casey snorted and rolled her eyes. "Please give me a little more credit than that. It's just…I'm tired of this stupid game. I want to go home for Christmas with nothing to worry about but eating too much turkey or whatever." She huffed and scowled at Derek's hockey bag, which was sitting by the door, ready for his afternoon game. She didn't notice the shrewd look Lisa gave her. "Look, Casey, I will not let you give up now. You've got this in the bag! I mean, he even looks at _you_ like he wants to devour you half the time."

"_What_?" Casey screeched. It was worse than she'd imagined if even Lisa could see it.

"I just mean that if he's desperate enough to want to hump his own sister-"

"Step. And that's disgusting."

"Same difference. All you have to do is just nudge him in the right direction, you know? Take advantage of the situation."

Casey scowled. Hadn't she been doing that already? "And what would you have me do?" she asked peevishly. Lisa shrugged. "I'm sure you can think of something. Let him see you naked by accident. It doesn't really matter, I just don't want to see you lose. I've seen him hold things over your head from when you were in high school – he would _never _let you forget this."

Well she was right about that, Casey mused. In fact it was the only reason she could use to justify not giving up. _Don't forget about all the things you wanted him to do last night_…her traitorous mind whispered. She glared at the thought and pushed it aside. She was stronger than this, damn it! And, really, this attraction to Derek wasn't all that surprising as he was the only male she had access to on a regular basis who she was actively trying to seduce without _actually _seducing. "I'm so confused!" she wailed miserably.

"Casey, relax," Lisa soothed. "You have to admit you've been having fun with this bet. Watching him squirm every time a girl walks by is really entertaining."

"I guess…" Casey sighed. "Fine, but if this isn't resolved by Friday, I really will give up."

She was still on the couch contemplating her conversation with Lisa when Derek came in. "What's up with you?" he demanded, pausing at the foot of the stairs. She snorted inwardly – like he didn't know. "I'm sick," she muttered. "In the head."

"What?"

She rolled her eyes, suddenly tired of him and anything related to this game for the moment. "Nothing. Aren't you going to be late for hockey?" He gave her a funny look, then shook his head and went up the stairs. She watched him go and decided a little exercise wasn't such a bad idea. Going for a run might clear her head some, and it did, when she got out there. She focused on the biting cold on her cheeks and the crunching snow under her feet, and ran as far as she could. She wasn't headed in any particular direction, but when she passed by the arena where Derek was playing his game, she wondered what her subconscious was telling her.

"Casey!" It was Danielle, from her economics class, and a blonde girl near the entrance. Since her lungs were burning anyway she stopped to say hello. "What're you two doing here?" Danielle shrugged. "Watching the game. One of my friends is playing and he badgered us into coming." She paused. "I didn't take you for a runner."

Casey shook her head. "I'm not, I just have a lot on my mind." Danielle nodded wisely. "That thing with Derek still going on?" The look on Casey's face must've given her away because Danielle laughed. "Poor you."

"What thing?" the other girl asked, suddenly interested in the conversation. Danielle introduced them. "Casey, this is Kate."

"Hi." She paused and sighed. "I have this bet with my…roommate –" Friends wasn't really accurate and to call him her step-brother after all that had happened lately made her feel dirty in a bad way. She outlined the basic parameters of the game and watched Kate's brows inch higher and higher. "Wait…" she said slowly. "You don't mean Derek Venturi, do you?"

Casey sighed. _Of course._ "Uh huh."

"He's playing today. He's pretty hot."

The cold was starting to seep in, now that she wasn't moving. She bounced from foot to foot. "Ah, I guess," she said half-heartedly, trying to pretend she'd never noticed – which, to be fair, she never _had_ until recently.

"You know," Kate said thoughtfully. "I could help you out, I think." Casey exchanged a glance with Danielle, who shrugged. "How?"

"I was planning on inviting him out after the game anyway, and after that, well…" she trailed off, but had that smile that only the most confident girls got in situations like this. Kind of like Kendra, Derek's old girlfriend.

"I –" she hesitated. _What are you doing? This is what you've been waiting for! _"Um, ok. Yes." She slapped on a grin. "That would be awesome, actually!" Kate looked smug and Casey had the fleeting thought that this girl was trouble with a capital T, but that wasn't really her problem. "I mean, only if you want to."

"Oh, I want to," Kate assured her. "We'd better get back in there though. Danielle can tell you all about it later!" Danielle looked kind of taken aback by the sudden development and offered Casey a feeble wave as she followed Kate back inside. Casey stood there for a moment, one hand pressed to her stomach. She felt kind of sick at the thought of blonde, man-eating Kate getting her hands on Derek. Not because she was worried about him, but because Kate was just the kind of girl he'd go for. Unbidden, the image of Derek putting his hands on that girl the way he had to her the other night sprang to mind and jealousy bubbled up in her chest.

"Oh _god_," she groaned. _Screw the run_, she thought. _I want a drink._


	4. Chapter 4

Derek trailed into the bar behind Kate, the hockey groupie who'd practically demanded he go out with her after the game. He'd tried to beg off, citing the exam he had in the morning which he needed to study for, but she wouldn't hear of it. He'd only really agreed because his buddy Mike and that girl Danielle were going too, and he wanted to avoid going home because he had no idea what to say to Casey, mostly because he had no idea what the fuck was going on anymore. _It's all fun and games until someone loses their mind. _

This stupid game was getting completely out of control. At first it had seemed harmless, even kind of fun, as most competitions with Casey were. Even when the unexpected attraction to her had started it wasn't that big a deal. But last night had been a game-changer, because even though he'd barely touched her, she'd _let _him. That alone should make him give up and take advantage of what Kate was clearly ready to offer, if only to restore balance to his world. And yet he wasn't going to lay a finger on her.

He scowled into his drink and tossed the rest of his beer back like it was water. _Goddamn Casey_, he thought, and along with the curse thought of Casey with her secret tattoos, and in her underwear, and the look in her eyes last night. He even thought of the way they'd wrestled around in the snow that morning, and the fact that _that_ was on his mind worried him the most. Then, as if he'd conjured her out of thin air, Derek saw her across the bar. She was still in the outfit she'd left to go running in earlier that day and was playing darts by herself, a half-empty pitcher of beer on the table next to her.

"What's she doing here?" he said, mostly to himself. Danielle heard and followed his gaze. "Looks like she's playing darts," she said. "What do you care?"

Derek glared at the challenging tone in Danielle's voice but said nothing. There was no way on earth he'd be able to explain it to her so he forced himself to focus on Kate. He pretended to be interested in her inane chatter and even managed to have a half-decent conversation with Mike, but every few minutes he couldn't help but find Casey in the crowd and wonder what she was doing there. Kate, who'd grown bored with him and turned her attention to Mike, didn't notice, but Danielle did. "Oh, for god's sake," she muttered to him. "Just go talk to her and get it over with." He didn't bother pretending she was wrong and slid out of the booth.

"Hey Case," he said as he strolled up. She offered him a quick sideways glance before hurling the last dart at the board. "What do you want?" she snapped, and he could tell immediately that she was drunk. He held up his hands in surrender. "I come in peace, honestly."

"Whatever."

Derek smirked. Drunk Casey was an interesting study: she could be surly and belligerent and mean, just about the exact opposite of her sober self. And while sober Casey got verbal diarrhea on a regular basis, getting more than a few complete sentences out of drunk Casey was like pulling teeth. "How long have you been here?"

She emptied the pitcher into her glass. "Not long enough."

"Uh huh." He pried the glass from her hand. "Hey!" she said indignantly. "Seriously, can't you just leave me alone for _one _night?" He went on as if she hadn't spoken. "Since when do you drink alone?" She grabbed the darts again and started throwing. "Since _you _started _ruining _my _life._" Derek felt something inside him twinge when she said that, and the feeling caught him completely off guard. "You'll have to narrow it down, Princess," he snapped, his back up. "I've 'ruined your life' plenty over the last eight years. At least, according to your diary in high school." He didn't know why he'd thrown that in, or why he was suddenly on the attack, but he couldn't seem to help himself. Surprisingly Casey didn't even acknowledge the crack about her diary, instead reaching around him to grab her glass. "Fine, is six weeks ago narrow enough for you?"

He blinked, then let out a short, mirthless laugh. "I ruined your life because you haven't been able to get laid? That's what this is about?" The same spot that had twinged when she'd accused him was suddenly taken over by a feeling he couldn't identify, except that he didn't like it or its implication. She jabbed a finger into his chest. "First of all, fuck you. Second, I couldn't give a shit about not being able to sleep with some random guy." He reached up to grab the hand that was still poking him and squeezed it tightly, leaning into her almost menacingly. "Then how _exactly _have I ruined your life?" She glared back. "Because I can't stop –"

But she did stop. She caught herself before she could finish the thought and snapped her mouth shut. _She can't stop __**what?**_ She yanked her hand out of his and turned on her heel to face the dartboard, as if the entire exchange hadn't just happened. "Shouldn't you get back to your date?" she asked calmly, only smiling slightly when she struck the bullseye.

"What date?" he asked furiously. Something big had nearly happened there, he could feel it. Casey spared him a glance and jerked her chin toward the booth he'd been sitting in. "Blondie over there. You came in with her."

"It's not a fucking date," he snarled.

"Sure looks like one," Casey shrugged, but Derek didn't miss the glare she shot over towards Kate, who by the looks of it hadn't even noticed he wasn't still sitting there. He smirked. "If I didn't know better I'd say you were jealous." The corners of her mouth turned down, but it took her an eternity to reply. "But you do know better," she said finally, sighing. "I'm going home."

"I'll take you," he said immediately, but she shook her head. "_No._ I'll call a cab. I just want to be alone for a while." And with that she weaved her way through the crowd, only slightly unsteady on her feet, and disappeared out the door. All he could do was watch her go, his thoughts whirling. What had just happened? She hadn't said it outright, but had she just intimated that he was getting to her as much as she was to him? He wandered back to the table to tell everyone he was leaving and ended up giving Danielle a ride home (as Kate and Mike would obviously be leaving together). As he pulled up to her place, she hesitated before getting out of the car. "Derek, I can't believe I'm telling you this, but maybe you should know. Me and Kate saw Casey earlier today and we got to talking about your bet. Kate offered to try and help Casey by taking you out or whatever."

"Oh yeah?"

"Yeah, and Casey wasn't happy about it. She probably just said yes to save face."

"Why _are _you telling me this?"

Danielle grimaced. "I have no idea. I don't even like you."

Derek snorted out a laugh at that, appreciating her honesty. "So Casey tried to set me up again?"

"No, she got roped into it. She's obviously got issues when she runs straight to a bar for four hours after letting some girl go after you."

Especially when _she_ was Casey MacDonald, he mused as he drove away. Unfortunately Danielle's confession only served to confuse him even more. How the hell was he supposed to feel about Casey's possible jealousy? Smug? Weirded out?

_Happy._

"Oh fuck me," he groaned.

* * *

Wednesday greeted Casey with a killer headache and an overwhelming annoyance with herself. One of her great failings as a drinker was that she never forgot anything. She remembered every humiliating antic and, in the case of last night, everything she said that she wished she hadn't. She'd nearly spilled to Derek that she couldn't get him out of her head, and she hadn't been very subtle about her opinion of Kate. She heaved a sigh and decided the best she could hope for was that Derek hadn't noticed her near slip-up, and lay in bed pouting about her headache for a while longer before dragging herself to the bathroom for some Tylenol.

The house was strangely quiet, she thought, then remembered that both Lisa and Derek were writing their last exams this morning. So she got a bowl of cereal and settled into the couch for the long haul, flipping through the channels until she found some kind of romantic Christmas movie. It was the typical story about two people who pretended to hate each other but then got together in the end, and the parallel between the movie and her own life was not lost on her. She glowered at the screen. "Don't be an idiot," she told the main character. "He's no good for you, and this will end _badly_, just you watch." But of course they got together anyway. "This is ridiculous," she grumbled and flipped around until she found The Grinch, which was a much better fit for her mood.

She pretended not to notice when Derek came in until he collapsed on the couch next to her, digging into a bag of chips. "What're you watching?"

"A movie," she said shortly.

"Looks lame," he remarked around a mouthful of Doritos and made a grab for the remote. She kicked his hand out of the way and pushed him back with her feet. "Forget it, I was here first." He regarded her feet resting on his leg with mock-horror. "Ugh. Get your gross, smelly feet off of me."

"My feet do _not _smell," she informed him haughtily and made no move to lift them off of him. "If you don't like it, leave." He said nothing, but shoved her feet away. She promptly dropped them back on his thigh and began to relax minutely. This she could do, this bickering with Derek was the norm - it was reassuring - so she decided to attempt a conversation. "How'd your exam go?" He shrugged. "Okay, I guess. I probably won't fail, if that's what you're wondering." She rolled her eyes and nudged him with a heel. "You know I don't think you're going to fail. I realize that you're not as dumb as you like to act." At that he tore his gaze from the TV and nearly smiled. "Gee, I didn't think you cared," he mocked. She sighed dramatically and turned her attention back to the movie. "I was wrong, you are an idiot." She didn't notice him smile at that, or that he shifted around to make her feet more comfortable on his lap; she only noticed the oddest sense of contentment, but shrugged it off after a minute or two as a weird side effect of her hangover.

By some miracle Casey managed to put her newfound attraction to Derek out of her mind for the rest of the afternoon, and it stayed that way until just after dinner, when Derek was chatting with her mom on his laptop. They were discussing the upcoming Christmas vacation while she puttered around the kitchen, tidying up the mess from dinner, when Nora said something that stopped Casey in her tracks. She rushed over to the computer and leaned in close over Derek's shoulder. "_What _did you just say?"

Nora grimaced apologetically. "It's the perfect storm of holidays. Everyone's coming to stay. My mom and my sister, and even George's parents are coming down from Barrie for a couple of nights." Casey didn't care about that, she only focused on one point. "Aunt Fiona's staying over? Why? _Please _don't tell me Vicky's coming too."

That was the last thing she needed, her bitch of a cousin getting involved. Thankfully Nora shook her head. "No, she's going skiing in Quebec, which is why Fi wants to stay a few days. She doesn't want to be alone." Casey braced one hand on the table and the other on Derek's shoulder. "Well thank god for small miracles." Then, "Wait, where's everyone going to sleep?"

It was as she leaned in closer to the screen to glare skeptically at her mother that Casey noticed two things. One, whatever shampoo or deodorant or cologne Derek used smelled incredible, and two, in her attempts to get closer to the computer she'd draped herself over his back. That in itself wasn't the issue, what _was_ was that she hadn't bothered to change out of her pajamas that day and as a consequence her very braless breasts were now pressed up against Derek's very tense back. He must have realized their situation at the same time as she had because he was taking great care not to move a muscle.

For reasons that escaped her at the moment, she stayed exactly where she was and pretended to listen to what her mother was saying. She was hyperaware of the heat radiating through his thin cotton shirt, and that after a second he seemed to relax minutely and lean back into her, just a little. Her heart skipped a beat and she glanced over to find him watching her. It would be so, so easy, she thought, to just do it, to kiss him.

"Hey, hello?" Nora was waving her hands on the screen. "Is this thing working? Can you guys hear me?" Casey expelled the breath she didn't realize she was holding and reluctantly turned back to face the computer. She immediately felt her body protest when she stepped back from Derek. "Sorry, must be a glitch. What were you saying?"

"Just that we'll figure something out for the sleeping arrangements. Anyway, I have to go, but I can't wait to see you guys on Friday. Love you both."

"Bye." As Derek signed off, Casey hurried over to the sink to wash the dishes. Any excuse to stay away from him at this point was a good one. Frankly she couldn't believe she'd just entertained the idea of _actually_ kissinghim, even for a split second – and not because of any dumb game, but simply because she'd wanted to. Looking as troubled as she felt, Derek came over and leaned against the counter. "Case…I–"

She could scarcely bring herself to look at him. "Yeah?" He seemed to wrestle with himself before he shook his head a little. "Ah, thanks for dinner."

"No problem," she said, both relieved and disappointed, but he was already hurrying out of the room. She took her time finishing up the dishes as she mulled things over. It was becoming obvious that something was going to give between her and Derek sooner or later. It was probably just a matter of time. The question wasn't how to stop it, but would it be _so _terrible if something did happen? What was one measly kiss in the grand scheme of things? It wasn't like she was going to sleep with him, she just needed to get him out of her system. Of course there was the small chance that she'd been misreading him and he _wasn't _attracted to her, in which case kissing him would be a disaster. She wanted to growl in frustration. Derek really was ruining her life.


	5. Chapter 5

Derek stared at the wall separating his room from Casey's and wished with every fibre of his being that he could read minds. This situation with Casey had spun so far out of control that there weren't words for it anymore. If he were to look at it logically, nothing serious had happened, only a few close calls and charged moments. But there was zero room for logic at this point because he was starting to think he _felt _something for her. An attraction to her was one thing, and it was easy to explain, but it was moments like that morning when they were hanging out watching movies and she'd had her feet on him that he'd liked. Moments like when he was talking to Nora and Casey'd leaned up against him, and yeah, he'd gotten a little thrill out of it, but it was just being close to her that had got to him the most. He could think of only one other person in his life that had affected him like that, and he'd nearly moved across the country for her.

Derek pulled a pillow over his face and debated if smothering himself and just ending it all would be the better option.

The worst part of it was that he wasn't sure that Casey wasn't just playing him. She'd been a lot more proactive in tempting him in this game than vice versa, so maybe this was just another tactic? He sighed and threw the pillow aside. _No, probably not_. He was reasonably sure that the way she'd been acting lately wasn't a part of the game, especially after what Danielle had told him, and how Casey had acted last night in the bar. He just wasn't confident enough to do something about it. No, the best thing to do was to ignore whatever ludicrous feelings he thought he had and pretend everything was normal.

_Yeah, good luck with that_, his inner voice taunted.

* * *

Casey was already dressed and eating breakfast when she heard Derek moving around upstairs, presumably going in for a shower. She hadn't slept much the night before and was up at the crack of dawn, early enough to see Lisa off for her morning run. She'd also finished packing and had her bags ready to be loaded into the car despite the fact they weren't leaving until the next morning. And, as usual, she was trying and failing to not think about Derek and their situation. She'd nearly come to accept that she wanted him, game or no game, but the logical part of her mind was staunchly refusing to accept it was anything more than physical. Because there was absolutely _no _way she could possibly feel anything else for the smug, arrogant, man-slut she called a step-brother.

Nope. No way.

Right?

She sighed and dumped her dishes in the sink before trudging up the stairs. It was sheer bad luck that her timing coincided with Derek coming out of the bathroom, shirtless and rubbing his damp hair with a towel. He caught sight of her and after a second's hesitation smirked and flexed his muscles.

"Morning Princess…Like what you see?"

Casey bit back a smile and couldn't help but give him an exaggerated once-over, like he'd done to her the other day after the underwear incident. Hockey had been very kind to him, she had to admit. He'd filled out quite a bit over the years and it struck her like a bat to the head that Derek wasn't a boy anymore, he was a _man._ She opened her mouth to give some smart, sarcastic reply, but instead said: "What if I do?"

She wasn't sure who was more surprised by that comment between the two of them. Sure, she'd nearly talked herself into taking action last night, but realistically that was the last thing she would have expected to come out of her mouth under _any _circumstance. And in most circumstances Derek would have smirked and fired back some lame comment about how irresistible he was, but now he looked more serious than she'd ever seen him. He took half a step toward her and her breath caught in her throat. She pressed her hand to his chest to stop him, afraid of him coming any closer. He came closer anyway, and she didn't move her hand. In fact she was having a hard damn time stopping her fingers from roaming across the broad expanse of his chest.

He reached up to comb back a few strands of her hair and she couldn't help but lean into his hand just a little. "Casey," he said quietly. "_What_ are we doing?" She was afraid to meet his eyes but forced herself to look up. "I don't know, Derek." Her heart was pumping like a jackhammer, and so was his by the feel of it under her hand. "I know what we should be doing," he said quietly. "But I also know what I want to do." Then he brushed his thumb over her lips and she nearly lost it.

"And what's that?" she murmured, too stunned to move. He said nothing but continued to trace her mouth with this thumb. She could feel the tension rolling off of him and realized they had officially crossed _that _line, the one she'd refused to acknowledge the existence of until this game had started but was now willing to admit might have been there for a long time before. As if it had a mind of its own, her hand moved from his chest and trailed down his abdomen to hook a finger in the waistband of his pants. She tugged ever so slightly and brought him another step closer. They were thigh to thigh now, chest to chest. It was the ultimate game of chicken and neither one wanted to give in first. Good god, she had never wanted anything more in her life than for him to kiss her in that moment. But then the door banged open at the bottom of the stairs and Lisa came stomping in, and Casey nearly wept with relief (frustration?) as the moment was broken. Derek dropped his hand and stepped back, his dark eyes never leaving hers. She wordlessly turned and went into her room, closing the door soundly behind her.

Derek stared at Casey's bedroom door for a moment as the need and the want raged in him. What the fuck had just happened?

"Morning!" Lisa said cheerfully as she came up the steps. He shot her a look so full of loathing that she actually recoiled. "Jesus, what crawled up your ass?" He could have happily throttled her right then – if not for her coming in and interrupting the moment, he and Casey would be –

He cut the thought off and stormed into his own room, slamming the door behind him. He wanted to yell or to hit something, or… no, what he really wanted to was to go into Casey's room and finish what they'd started out in the hall. But of course he couldn't. He threw himself onto his bed, and his fingers itched to reach for his phone to call somebody, _anybody _who could set him straight. He was not allowed to want his step-sister so badly, especially one he'd considered his greatest foe for so many years. He considered calling Sam but the thought of trying to get the words out made his throat close up. Sam wouldn't really understand…no one would. He tried to distract himself with video games, then he completely cleaned his room, shoveled half the neighbourhood, and finally got around to packing. It was as he was unceremoniously shoving things into his bag that there was a tentative knock on his door. He glanced over and his jaw tightened. "Hey."

Casey didn't make a move to actually cross the threshold but stood in the frame with her arms crossed so tightly her fingers probably met on the other side. "Hey. Um." She took a deep breath and focused on the mess in his suitcase. "We need to talk." Four of the most hated words in the English language, yet all he could think was: _No shit, Sherlock._ Derek Venturi was not a talker, especially when it came to feelings, but there was no getting around it this time."Yep."

She inched forward a couple of steps and cast a quick glance across the hall at Lisa's closed door. The indecision was written all over her face but she pushed his door shut. "So?" he said, and she finally looked at him. "Why do I have to start?"

He shrugged petulantly. "You came to me, remember?"

"Yeah, well, I guess I'm just braver than you." It might have been considered a dig once upon a time, but in this situation he took the comment at face value and sighed. "Yeah, I guess you are." That seemed to boost her confidence some and she came over to the bed and started taking the mountain of clothes out of his bag to fold them. "This has to stop," she said finally, after she'd made a neat pile out of his shirts. He'd been expecting it, of course, but his heart still constricted and he couldn't help but be difficult about it. "What does, exactly?"

"Oh, don't even," she huffed, but waved a finger between the two of them. "This. The game. Us. You know what I'm talking about." He wanted to feign ignorance or tell her she was crazy, but instead his shoulders sagged and he gave a jerky nod. "Yeah, no kidding." There, he'd acknowledged it, and his saying it out loud seemed to burst whatever dam Casey had set up to hold herself together.

"I mean, it's _crazy_, right? I don't even understand how it happened!"

The memory of that night in the kitchen when he'd wanted to see that tattoo of hers flashed in his mind. That was the start of the attraction for him, but he didn't tell her that. "It must just be because of the bet, you know?" he said quietly. He desperately wanted to believe that, but deep down he knew there was more to it. Just because a girl was hot did not mean he developed feelings for her. She hesitated, then shrugged. "I guess, which is why I'm calling it off. I just…things need to be normal again, you know?" He opened his mouth to say, yes, you're right, I completely agree, but instead he heard himself say: "how _can _they?"

"What?" she said warily. He started pacing. "Casey, how can things possibly go back to normal after this? Do you know how many times over the last few weeks that I've wanted you? I can't erase that."

"I know!" she said angrily. "I know that, okay? I can't get you out of my head, Derek, and it's driving me nuts! That's not going to stop just because the stupid game does!" Derek stopped to stare at her. She looked furious and embarrassed and ready to bolt. Finally he threw up his hands. "Oh, fuck it," he said, and kissed her.

* * *

A huge part of him hoped that he would feel nothing, that by kissing her he could get her out of his system. He was sorely disappointed. He felt…well, there weren't words to describe it, and when Casey wrapped her arms around his neck and deepened the kiss, heat coursed through him so fast he thought he would burst. He wanted to lift her up and have her legs wrap around his waist and to take her to bed, and because of that he very reluctantly put his hands on her hips and pulled back. She was pink-cheeked and breathing heavily and stared up at him, clearly shocked. "I guess it's a draw?" she said finally. "Guess so," he replied lamely. She fumbled with the door and left without another word, and he sank down onto his bed. Oh, this was _bad_.


End file.
